Wireless communication system and wireless communication method

ABSTRACT

A wireless communication system includes a pilot addition decision portion for deciding whether to add pilot symbols which are separate from the basic pilot symbols, to frames; a control symbol generation portion for generating control symbols including information related to additional pilot symbols; a frame assembly portion for assembling frames to which pilot symbols are added according to pilot addition decision; a transmission portion for transmitting the frames; and the reception device includes a control symbol demodulation portion for demodulating control symbols included in the received frames, and judges whether or not additional pilot symbols are included in the received frames based on the control symbol information; a data symbol demodulation portion for demodulating data symbols based on a propagation path estimation value which is estimated using the additional pilot symbols or using the additional and basic pilot symbols when the additional pilot symbols are included in the received frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/648,561 filed on Dec. 29, 2009, now pending, which is a continuationof U.S. application Ser. No. 11/878,060 filed on Jul. 20, 2007, now U.S.Pat. No. 7,643,570, which is a continuation of International ApplicationNo. PCT/JP2005/001577, filed Feb. 3, 2005, the contents of each areherein wholly incorporated by reference.

TECHNICAL FIELD

This invention relates to a wireless communication system and wirelesscommunication method, and in particular relates to a wirelesscommunication system and wireless communication method for transmittingand receiving frames comprising basic pilot symbols used for propagationpath estimation, control symbols which convey control informationnecessary for data channel demodulation, and data symbols which conveyinformation bits.

In order to increase the efficiency of data packet transmission inpacket transmission for cellular mobile communication, adaptivemodulation/demodulation control, adaptive spreading factor control,transmission power control, HARQ (Hybrid Automatic Repeat reQuest)control, scheduling control, and other types of adaptive wireless linkcontrol are employed. These types of control are performed using acontrol channel which is transmitted with the data channel; thetransmitting station uses the control channel to notify the receivingstation of the wireless link parameters being used in the data channel.For example, in the case of adaptive modulation/demodulation control,the control channel transmits the data channel modulation method (QPSK,16QAM, or similar) and the coding rate. In the case of adaptivespreading factor control, the control channel transmits the spreadingfactor and spreading code, or the number of symbol repetitions and otherinformation. In HARQ control, the control channel transmits the packetnumbers transmitted over the data channel, the number ofretransmissions, and other information. In the case of schedulingcontrol, user IDs and other information is transmitted using the controlchannel.

FIG. 22 shows a frame configuration of the prior art, used in packettransmission for cellular mobile communication. One frame comprisesbasic pilot symbols S_(P), control symbols S_(C), and data symbolsS_(D). In a downlink in which a base station performs transmission, thebasic pilot symbols S_(P) may be regarded as common pilot signals. Basicpilot symbols S_(P) are employed for propagation path estimation whichis necessary for demodulation of control channel and data channelsignals. In the data channel, adaptive wireless link control is employedto execute control of the modulation method, coding rate, spreadingfactor, transmission power, and similar. These control parameters areconveyed by means of control symbols S_(C).

In adaptive wireless link control, control is executed to improve thedata channel communication quality of a user experiencing poorcommunication quality at the edge of a cell, or to switch to atransmission method in which errors do not occur in an environment withpoor communication quality, or similar. FIG. 23 is an example of a casein which transmission power control is performed for a user experiencingpoor communication quality, at a cell edge or similar. As indicated inFIG. 23, in downlink communication control is executed so that the basicpilot symbol power is held constant, while the control symbol and datasymbol transmission power is increased. In this way, in the example ofFIG. 23, through transmission power control of the control channel anddata channel, control is executed to improve communication quality; butadaptive control of basic pilot symbols is not performed. Henceordinarily, in downlink communications, somewhat higher transmissionpower is allocated to the basic pilot symbols. However, at a cell edgethere is the effect of interference from other cells, and so there is atendency for channel estimation precision based on the pilot symbols tobe degraded due to interference from other cells.

FIG. 24 is an example of a case in which adaptive spreading control isperformed for a user at a cell edge or similar, experiencing poorcommunication quality. In this example, by increasing the number ofrepetitions of data symbols, the S/N of data channel is improved. Thusin the example of FIG. 24 also, control is executed to improvecommunication quality by controlling the number of symbol repetitions inthe data channel, but adaptive control to improve the S/N of pilotsymbols is not performed.

In this way, in conventional packet transmission methods thecommunication quality in the data channel between a user terminal at acell edge or similar with poor communication quality and a base stationis ensured through adaptive wireless link control, but there haveexisted no mechanisms for performing adaptive control of the pilotsymbols, which greatly affect demodulation characteristics. Hence theestimation precision of channel estimation values used in datademodulation has not been improved, and so there has been the problem ofa limit to improvement of the demodulation characteristics of the datachannel.

In a first technology of the prior art, prescribed control symbols, suchas for example the TFCI (Transport Format Combination Indicator) controlsymbols stipulated by 3GPP standards, are used as pilot symbols inaddition to regular pilot symbols (see for example JP 2003-32146 A). Bymeans of this first technology of the prior art, as a result of anincreased number of symbols used as pilot symbols, the channelestimation precision can be improved.

As a second technology of the prior art, in a LAN format having apreamble portion and a payload portion, pilot symbols are inserted intothe payload portion as well as into the preamble portion (see forexample JP 2003-536288 A or WO01/059950 based upon PCT/US01/03778).

However, in the first technology of the prior art, the insertion ofadditional pilot symbols is not performed adaptively. And in the firsttechnology of the prior art, the properties particular to the 3GPPstandard are utilized, so that general application to channel estimationfor wireless communication is not possible.

The second technology of the prior art is not a method of adaptiveinsertion of additional pilot symbols, but of always inserting pilotsymbols into the preamble portion and into the payload portion, so thatthere is the problem that the number of pilot symbols increases andtransmission efficiency is reduced.

SUMMARY OF THE INVENTION

In light of the above, an object of the invention is to adaptivelyperform insertion of added pilot symbols based on the propagation pathstate, to improve channel estimation precision.

A further object of the invention is to adaptively improve channelestimation precision even when motion velocity is high and the fadingfrequency is high.

A further object of the invention is to control addition of pilotsymbols while relating this control to an adaptive control whichdetermines data symbol modulation method, coding rate, spreading factor,transmission power, and similar, based on the propagation path state.

A further object of the invention is to switch transmission system froma transmission system by a single transmission antenna to a transmissionsystem by a plurality of transmission antennas, such as MIMO(Multiple-Input-Multiple-Output), transmission-beam forming, andsimilar, based on the propagation path state or based on requests.

A further object of the invention is to enable the power of the basicpilot symbol and the number of the basic pilot symbols to be set inadvance to small values.

A further object of the invention is to enable channel estimation byidentifying the presence or absence of added pilot symbols, the numberof symbols, and the added positions on the receiving side, and usingadded pilot symbols.

This invention relates to a wireless communication system and wirelesscommunication method for transmitting and receiving frames comprisingbasic pilot symbols used in propagation path estimation, control symbolsconveying control information necessary for data channel demodulation,and data symbols conveying information bits.

In a wireless communication system of this invention, a transmissiondevice comprises a pilot addition decision portion that decides whetherto add to frames pilot symbols which are separate from basic pilotsymbols; a control symbol generation portion, which generates controlsymbols comprising information related to additional pilot symbols; aframe assembly portion, which assembles frames with the pilot symbolsadded according to the pilot addition decision; and a transmissionportion, which transmits the frames.

A transmission device further comprises a propagation path informationoutput portion, which acquires and outputs propagation path informationrelating to the state of the propagation path between the transmissiondevice and the reception device wherein the pilot addition decisionportion decides whether to add additional pilot symbols, and the numberof additional pilot symbols to add, based on this propagation pathinformation.

A transmission device further comprises a motion velocity acquisitionportion, which acquires the motion velocity of the reception devicewherein the pilot addition decision portion decides whether to arrangethe additional pilot symbols in dispersed positions in a data symbolarea, and positions of additional pilot symbols, according to the motionvelocity of the reception device.

Further, a transmission device comprises a propagation path informationoutput portion, which acquires and outputs propagation path informationrelating to the state of the propagation path between the transmissiondevice and the reception device, and an adaptive control portion, whichadaptively controls the transmission method based on the propagationpath information wherein the pilot addition decision portion decides toadd pilot symbols when transmission errors are not improved by theadaptive control.

Further, a transmission device comprises a plurality of transmissionantennas, and a transmission portion corresponding to the respectivetransmission antennas wherein in a case where pilot symbols are notadded, the frame assembly portion assembles a frame not comprisingadditional pilot symbols, to be transmitted from one transmissionantenna, and in a case where pilot symbols are added, assembles saidframe to be transmitted from the one transmission antenna, and frames tobe transmitted from other transmission antennas, comprising additionalpilot symbols, but comprising neither basic pilot symbols nor controlsymbols.

A reception device of a wireless communication system of the inventioncomprises a control symbol demodulation portion, which demodulatescontrol symbols included in the received frames and judges whetheradditional pilot symbols are included in the received frames based onthe control symbol information; a propagation path estimation portionwhich, when the additional pilot symbols are included, uses theadditional pilot symbols to estimate the propagation path; and a datasymbol demodulation portion, which demodulates data symbols based on thepropagation path estimation value.

The propagation path estimation portion of the reception devicecomprises a first propagation path estimation portion, which estimatesthe propagation path using the basic pilot symbols, and a secondpropagation path estimation portion which, if additional pilot symbolsexist, estimates the propagation path using the additional pilot symbolswherein the control symbol demodulation portion uses the firstpropagation path estimation values estimated by the first propagationpath estimation portion to demodulate control symbols, and the datasymbol demodulation portion uses the control symbol information and thesecond propagation path estimation values estimated by the secondpropagation path estimation portion to demodulate data symbols.

Further, a reception device comprises an error detection portion todetect errors in additional pilot information included in the controlchannel, and a second control symbol demodulation portion which, if notransmission errors have occurred in the additional pilot information,demodulates control symbols again based on the second propagation pathestimation values, and the data symbol demodulation portion demodulatesdata symbols using the control symbols demodulated by the second controlsymbol demodulation portion and the second propagation path estimationvalues.

A wireless communication method of the invention has, on thetransmitting side, a step of deciding whether or not to add pilotsymbols which are separate from basic pilot symbols, to frames a step ofgenerating control symbols comprising information relating to additionalpilot symbols when pilot symbols are added, and a step of assembling andtransmitting frames comprising the basic pilot symbols, control symbols,additional pilot symbols, and data symbols; and has, on the receivingside, a step of demodulating control symbols included in the receivedframe, a step of judging whether additional pilot symbols are includedin the received frame based on the control symbol information, a step,when additional pilot symbols are included, of estimating thepropagation path using the additional pilot symbols, and a step ofdemodulating data symbols using the propagation path estimation value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first summary diagram of the invention;

FIG. 2 is a second summary diagram of the invention;

FIG. 3 shows the configuration of a transmission device of theinvention;

FIG. 4 is an explanatory diagram of a pilot addition criteria table,stored in an additional pilot information storage portion;

FIG. 5 explains positions within data symbols for pilot addition;

FIG. 6 shows the first flow of processing for pilot addition control byan additional pilot allocation portion;

FIG. 7 shows the second flow of processing for pilot addition control bythe additional pilot allocation portion;

FIG. 8 shows the third flow of processing for pilot addition control bythe additional pilot allocation portion;

FIG. 9 shows the fourth flow of processing for pilot addition control bythe additional pilot allocation portion;

FIG. 10 shows a first configuration of a reception device;

FIG. 11 shows the flow of demodulation processing by a demodulationportion in a reception device;

FIG. 12 shows a second configuration of a reception device whichalleviates control channel errors;

FIG. 13 shows a frame configuration;

FIG. 14 shows the flow of demodulation processing in the demodulationportion of the reception device of FIG. 12;

FIG. 15 shows the configuration of the transmission device of a secondembodiment;

FIG. 16 shows the frame configuration in the second embodiment;

FIG. 17 shows the configuration of the reception device in the secondembodiment;

FIG. 18 shows the configuration of the transmission device in a thirdembodiment;

FIG. 19 explains antenna beam directionality;

FIG. 20 shows the frame configuration in the third embodiment;

FIG. 21 shows the configuration of the reception device in the thirdembodiment;

FIG. 22 shows the conventional frame configuration used in packettransmission for cellular mobile communication;

FIG. 23 is a first frame example in a case in which transmission powercontrol is performed for users at a cell edge experiencing poorcommunication quality; and

FIG. 24 is a second frame example in a case in which adaptive spreadingfactor control is performed for users at a cell edge experiencing poorcommunication quality.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Summary of the Invention

Addition of Pilot Symbols

For a user terminal which suffers poor communication quality due tolocation at a cell edge, the base station that is the transmitting sideadditionally inserts pilot symbols S_(NP) which are separate from basicpilot symbols S_(P) in the area of data symbols S_(D), as shown in (B)of FIG. 1, and notifies the user terminal which is the receiving side ofinformation relating to these additional pilot signals S_(NP) by meansof control symbols S_(C). Conversely, when the user terminal becomes thetransmitting side, and transmits data to the base station, if thecommunication quality between base station and user terminal is poor,pilot symbols S_(NP) are additionally inserted into the area of datasymbols S_(D), and the base station which is the receiving side isnotified of this information by means of control symbols S_(C).

Additional insertion of pilot symbols S_(NP) is decided according to thestate of the propagation path between the transmitting station andreceiving station. The propagation path state between the transmittingstation and receiving station may be measured by the transmittingstation, or the results of measurement by the receiving station may befed back to the transmitting station. Parameters indicating thepropagation path state may include the reception power, SIR (Signal toInterference power Ratio), delay spreading, Dopper frequency (fadingfrequency), and similar. A threshold for communication quality may beprovided based on the measured results of such propagation pathparameters, and when the communication quality is equal to or less thanthe threshold, the transmitting station decides on additional insertionof pilot symbols. The Doppler frequency is used to estimate the motionvelocity of the mobile station or fading frequency.

Dispersion of Additional Pilot Symbols

When, among the propagation path parameters, the Doppler frequency ishigh, the propagation path fluctuations in the time-direction are rapid,and so the pilot symbols S_(NP) are added to the date symbols anddispersed in the time direction as indicated in (B) of FIG. 2, andchannel estimation is performed following propagation path fluctuations.

Control to Add Pilot Symbols in Connection with Adaptive Wireless LinkControl

The transmitting station performs adaptive wireless link control for thedata channel, and if further improvement of the communication quality ofthe uplink channel is no longer possible, additional insertion of pilotsymbols S_(NP) is performed. Also, when returning ACK/NACK signalsthrough the data channel in retransmission control, if the error rate isnot improved through adaptive wireless link control of the data channel,a decision is made for additional insertion of pilot symbols S_(NP).

Addition of Pilot Symbols During Control of Transmission from aPlurality of Antennas

When the transmitting station uses a plurality of transmission antennasfor transmitting data channel in accordance with MIMO multiplexedtransmission, transmission-diversity, transmission-beam forming andsimilar, pilot symbols different from the basic pilot symbols areadditionally inserted into the area of data symbols.

In MIMO multiplexed transmission and diversity transmission, mutuallyorthogonal pilot signals must be transmitted from each transmissionantenna. Consequently, orthogonal pilot symbols are inserted into thedata symbol area for each transmission antenna.

In transmission-beam forming, additional pilot symbols multiplied by thesame antenna weight as data symbols must be transmitted, and soadditional pilot symbols that are beam-formed by the same antenna weightas data symbols are additionally inserted into the data symbol area.

Reception Control

At the transmitting station, a decision is made as to whether to insertadditional pilot symbols and the number and positions of the additionalpilot symbols, according to the propagation path state, or whetheradaptive wireless link control parameters for the data channel can bemodified, or whether a transmission method using multiple antennas isused, and the receiving station is notified of this information via thecontrol channel.

In the receiving station, at first basic pilot symbols are used toperform channel estimation, and control channel demodulation isperformed based on the channel estimation value. Next, based upon thedemodulated control information, information such as the presence orabsence of additional pilot symbols, the number of additional pilotsymbols, and the additional pilot symbols positions is obtained. And inthe case where additional pilot symbols have been inserted, theadditional pilot symbols are used to again perform channel estimation.Finally, data channel demodulation is performed using the channelestimation values obtained using additional pilot symbols. Here, datachannel demodulation may be performed using channel estimation valuesonly for additional pilot symbols, or averages of additional pilotsymbols and basic pilot symbols may be used as channel estimationvalues. Channel estimation values only for additional pilot symbols areused when the fading frequency is high.

Control when there are No Transmission Errors in Additional PilotInformation

The control channel is divided into a portion comprising additionalpilot symbol information and another control information portioncomprising wireless link parameters. And when there are no errors inadditional pilot information, and there are errors in the other controlinformation of the control channel, the channel estimation valuesestimated using the additional pilot symbols are employed to againperform control channel demodulation, to alleviate the control channelerrors.

This invention relates to a wireless communication method having a frameconfiguration such as that shown in FIG. 1, and is not limited totransmission schemes used in communication. That is, this invention canalso be applied to a case in which one symbol shown in FIG. 1 ismodulated by multiple carriers, in addition to a case in which aresymbol is modulated by a single carrier. For example, when applying thisinvention to the OFDM (Orthogonal Frequency Division Multiplexing)transmission scheme, which is a multiple carrier modulation method, onesymbol in FIG. 1 is regarded as one OFDM symbol comprising a pluralityof sub carrier-components, and this invention can be applied.

(B) First Embodiment

(a) Configuration of Transmission Device

FIG. 3 shows the configuration of a transmission device of theinvention; the frame generation portion 11 has a basic pilot generationportion 11 a which generates basic pilot symbols, a control channelgeneration portion 11 b which generates control symbols, a data channelgeneration portion 11 c which generates data symbols, an additionalpilot generation portion 11 d which generates additional pilot symbols,and a multiplexing portion 11 e which performs multiplexing of thesesymbols. The frame generation portion 11 generates a frame such as thatshown in (A) of FIG. 1 and (A) of FIG. 2 when additional pilot symbolsS_(NP) are not added, and generates a frame such as shown in (B) of FIG.1 or in (B) of FIG. 2 when additional pilot symbols S_(NP) are to beadded, and outputs the frame. The transmission portion 12 orthogonallymodulates frames generated by the frame generation portion 11, andup-converts the baseband transmission signal frequency to the radiofrequency, amplifies the signal and outputs the result to the antenna13.

The adaptive wireless link control portion 14 performs control to decideon the data channel modulation method and coding rate, spreading factor,and other link parameters, according to propagation path informationindicating the state of the propagation path received from acommunicating terminal (receiving station), or propagation pathinformation indicating the state of the propagation path measured by thepropagation path state measurement portion 22 within the transmissiondevice itself, or ACK/NACK information received from the receivingstation, or a request from the receiving station. At the same time, thisdecided information is input to the control channel generation portion11 b and data channel generation portion 11 c. The adaptive wirelesslink control portion 14 also performs adaptive wireless link control ofthe data channel, and when the control to further improve thecommunication quality of the data channel is no longer possible, or whenthe error rate is not improved by retransmission control, information tothis effect is input to the additional pilot allocation portion 15.Here, the control for improving the communication quality is loweringthe modulation factor or reducing the coding rate, or increasing thespreading factor.

Based on the propagation path information (propagation path state), theadditional pilot allocation portion (pilot addition decision portion) 15decides to make space in the data channel and add pilot symbols(additional pilot symbols) which are separate from the basic pilotsymbols. Similarly upon being notified by the adaptive wireless linkcontrol portion 14 that further control to improve the data channelcommunication quality is no longer possible, or upon being notified bythe adaptive wireless link control portion 14 that the error rate is notimproved by retransmission control, the additional pilot allocation isdecides to add the additional pilot symbols to the data channel. Theadditional pilot allocation portion 15 also refers to a pilot symboladdition criteria table, stored in an additional pilot informationstorage portion 16, and based on the propagation path state (forexample, the reception SIR), decides on the number of additional pilotsymbols and the additional pilot symbols positions, and inputs theresults to the control channel generation portion 11 b, data channelgeneration portion 11 c, and additional pilot generation portion 11 d.

FIG. 4 explains the pilot symbol addition criteria table stored in theadditional pilot information storage portion 16; (A) of FIG. 4 is acorrespondence table between pilot symbol addition criteria and thenumber added, and (B) of FIG. 4 is a table of pilot symbol additionpositions and addition order. From the table in (A) of FIG. 4, when thereception SIR is equal to or above a prescribed value, no pilot symbolsare added, but when the reception SIR is equal to or less than aprescribed value, pilot symbols are added, and the poorer the receptionSIR, the greater the number of additional pilot symbols. As is clearfrom the table of (B) of FIG. 4, when the Doppler frequency is less than100 Hz, that is, when the motion velocity of the mobile terminal whichis the receiving terminal is slow, the additional pilot symbols are notdispersed; but when the Doppler frequency is 100 Hz or higher, that is,when the mobile terminal which is the receiving terminal is movingrapidly, the additional pilot symbols are dispersed and arranged. Thereason for dispersed arrangement is that the propagation path (channel)cannot be estimated with good precision by the fixed arrangement ofpilot symbols when the fading frequency is high due to the highvelocities.

FIG. 5 explains pilot addition positions among data symbols; (A)indicates pilot addition positions for the fixed arrangement, and (B)indicates pilot addition positions for the dispersed arrangement,showing addition positions for each of the cases in which the number ofadditional pilot symbols is one through four.

Returning to FIG. 3, the control channel generation portion 11 b createscontrol symbols comprising link parameters and information relating toadditional pilot symbols (whether additional pilot symbols are present,the number added, added positions), and the data channel generationportion 11 c creates data symbols based on the link parameters, whilealso creating data symbols such that no data symbols are arranged in theadditional pilot symbols positions indicated by the additional pilotallocation portion 15.

The reception portion 17 receives signals sent from the receivingstation via the antenna 18, down-converts the frequency of the receivedradio signals to the baseband frequency, and then performs orthogonaldemodulation and inputs the signals to the channel estimation portion19, control channel demodulation portion 20, and data channeldemodulation portion 21. The channel estimation portion 19 uses pilotsymbols to estimate the uplink propagation path (channel) from thereceiving station such as mobile terminal, and the control channeldemodulation portion 20 uses the channel estimation value to demodulatecontrol channel signals sent from the receiving station, and notifiesthe adaptive wireless link control portion 14 and additional pilotallocation portion 15 of the propagation path information transmittedvia the control channel as well as ACK/NACK and other information. Thepropagation path information is information indicating the state of thedownlink propagation path as measured by the receiving station. When thedownlink and uplink radio frequencies are not very different, and thedownlink and uplink wireless states can be assumed to be equivalent, apropagation path measurement portion 22 can be provided, which measuresthe propagation path state and notifies the adaptive wireless linkcontrol portion 14 and additional pilot allocation portion 15, and insuch a case the receiving station need not measure propagation pathinformation and provide feedback.

The data channel demodulation portion 21 uses the above channelestimation values as well as control information which identifies themodulation method, coding rate and similar to demodulate data symbolsand output the results.

(b) Pilot Addition Control

FIG. 6 shows the flow of processing for first pilot addition control bythe additional pilot allocation portion 15. Here dispersion control ofadditional pilot symbols is not performed.

The additional pilot allocation portion 15 acquires propagation pathinformation, such as for example the reception SIR (step 101), judgeswhether the reception SIR is less than a threshold (in the example ofFIG. 4, 10 dB) (step 102), and if the value is equal to or greater thanthe threshold, instructs the frame generation portion 11 not to addpilot symbols (step 103). If on the other hand the reception SIR is lessthan the threshold, then the number of pilot symbols to be added isdecided based on the reception SIR, referring to the table in (A) ofFIG. 4 (step 104), and the frame generation portion 11 is instructed tocreate a frame comprising this number of added pilot symbols (step 105).

When no pilot symbols are to be added, the frame generation portion 11creates a frame as in (A) of FIG. 1, and when pilot symbols are to beadded, creates a frame as in (B) of FIG. 1, and the transmission portion12 executes control to transmit the frame thus created (step 106).

By means of the above-described additional pilot control, insertion ofadditional pilot symbols is performed adaptively based on thepropagation path state, and the channel estimation precision can beimproved.

FIG. 7 shows the flow of second pilot addition control by the additionalpilot allocation portion 15, in a case in which additional pilot symbolsdispersion control is performed.

The additional pilot allocation portion 15 acquires propagation pathinformation, such as for example the reception SIR and Doppler frequency(step 201), judges whether the reception SIR is less than a threshold(step 202), and if the value is equal to or greater than the threshold,instructs the frame generation portion 11 not to add pilot symbols (step203). If on the other hand the reception SIR is equal to or greater thanthe threshold, the number of pilot symbols to add is decided based onthe reception SIR (step 204), and a judgment is made as to whether theDoppler frequency is less than 100 Hz (step 205). If the Dopplerfrequency is less than 100 Hz, so that the motion velocity of thereceiving terminal is slow, then an addition position decision is madesuch that additional pilot symbols are not dispersed (step 206), but ifthe Doppler frequency is equal to or greater than 100 Hz, so that themotion velocity of the receiving station is fast, then the additionpositions are decided such that the additional pilot symbols aredispersed (step 207), and the frame generation portion 11 is instructedto create a frame comprising the additional pilot symbols (step 208).

The frame generation portion 11 creates a frame such as shown in (A) ofFIG. 2 when pilot symbols are not added, creates a frame such as shownin (B) of FIG. 1 when pilot symbols are to be added but not dispersed,and creates a frame such as shown in (B) of FIG. 2 when pilot signalsare to be added and dispersed; the transmission portion 12 then executescontrol to transmit the created frame (step 209).

By means of the above pilot symbol addition control, even when themotion velocity of the mobile station is fast and the fading frequencyis high, by dispersing the positions of the additional pilot symbols,the channel estimation precision can be adaptively improved.

FIG. 8 shows the flow of processing for third pilot addition control bythe additional pilot allocation portion 15, performed in cases whenthere is notification from the adaptive wireless link control portion 14that control to further improve the data channel communication qualityis not possible.

The adaptive wireless link control portion 14 acquires propagation pathinformation (step 301), and performs adaptive control based on thepropagation path information (step 302).

In this adaptive control, the adaptive wireless link control portion 14checks, based on the propagation path information, whether the datachannel modulation method, coding rate, spreading factor, and other linkparameters can be modified (step 303); if parameters can be modified,these link parameters are modified (step 304). That is, the adaptivewireless link control portion 14 lowers the modulation factor and codingrate, or increases the spreading factor, when the reception quality ispoor. Then, data is transmitted according to this adaptive control (step308).

If on the other hand in step 303 the link parameters cannot be modified,the adaptive wireless link control portion 14 notifies the additionalpilot allocation portion 15 that adaptive control cannot be used tofurther improve the data channel communication quality (step 305).

Upon being notified by the adaptive wireless link control portion 14that further improvement of the data channel communication quality byadaptive control is not possible, the additional pilot allocationportion 15 decides the number of pilot symbols to add and the additionpositions based on the reception SIR (step 306), and instructs the framegeneration portion 11 to create a frame comprising the number of pilotsymbols to be added, in the addition positions (step 307).

the frame generation portion 11 creates a frame as in (A) of FIG. 1 whenpilot symbols are not to be added, and creates a frame as in (B) of FIG.1 or (B) of FIG. 2 when pilot symbols are to be added, and thetransmission portion 12 executes control to transmit the created frame(step 308).

According to the above-described pilot symbol addition control, throughthe control to add additional pilot symbols in conjunction with theadaptive wireless link control of the data channel, not only can the S/Nof data channel be improved, but the precision of channel estimation cansimultaneously be improved, so that system throughput can be enhanced.

FIG. 9 shows the flow of processing for fourth pilot addition control bythe additional pilot allocation portion 15, when there is notificationfrom the adaptive wireless link control portion 14 that the error ratecannot be improved through adaptive control.

The adaptive wireless link control portion 14 acquires ACK/NACKinformation (step 401), and based on the ACK/NACK information judgeswhether there are transmission errors (step 402); if there are notransmission errors, the transmission portion 12 executes control totransmit the created frame (step 403).

If on the other hand there are transmission errors, the adaptivewireless link control portion 14 checks whether link parameters, such asthe spreading factor, can be modified (step 404), and if modification ispossible, performs modification so as to increase the spreading factor(step 405). Spreading factor control can be performed by increasing ordecreasing the number of data symbol repetitions. Then, the transmissionportion 12 executes control to transmit the created frame (step 403).

If in step 404 modification of the spreading factor is not possible, theadaptive wireless link control portion 14 notifies the additional pilotallocation portion 15 of the fact that the error rate cannot be improvedthrough adaptive control (step 406).

Upon notification from the adaptive wireless link control portion 14that the error rate cannot be improved through adaptive control, theadditional pilot allocation portion 15 decides on the number of pilotsymbols to be added and the addition positions based on the receptionSIR (step 407), and instructs the frame generation portion 11 to createa frame comprising the number of pilot symbols to be added in theaddition positions (step 408).

The frame generation portion 11 creates a frame such as in (A) of FIG. 1when pilot symbols are not to be added, and creates a frame such as in(B) of FIG. 1 or (B) of FIG. 2 when pilot symbols are to be added, andthe transmission portion 12 executes control to transmit the createdframe (step 403).

By means of the above-described pilot symbol addition control, pilotsymbols are added when transmission errors are not alleviated, so thatthe S/N of data symbol can be improved through adaptive control, and inaddition the channel estimation precision can be improved through pilotaddition.

(c) First Configuration of a Reception Device

FIG. 10 shows a first configuration of a reception device. The receptionportion 31 receives signals sent from the transmission device (forexample, abase station) via the antenna 30, down-converts the frequencyof the received radio signal to the baseband frequency, and thenperforms orthogonal demodulation of the received frame and inputs theresults to the first channel estimation portion 32 a, control channeldemodulation portion 32 b, second channel estimation portion 32 c, anddata channel demodulation portion 32 d of the demodulation portion 32.

The first channel estimation portion 32 a uses the basic pilot symbolsincluded in the received frame to perform channel estimation, andoutputs the first channel estimation value thus obtained. The controlchannel demodulation portion 32 b demodulates the control channel basedon the first channel estimation value, and based on the additional pilotinformation included in the demodulated control channel, confirmswhether additional pilot symbols are present and the positions thereof,and if additional pilot symbols are included, instructs the secondchannel estimation portion 32 c to execute channel estimation using theadditional pilot symbols. The control channel demodulation portion 32 balso notifies the data channel demodulation portion 32 d of the datachannel adaptive wireless link parameters and additional pilot symbolposition information.

The second channel estimation portion 32 c performs channel estimationusing the additional pilot symbols according to the instruction from thecontrol channel demodulation portion 32 b and inputs the second channelestimation value thus obtained to the data channel demodulation portion32 d. The second channel estimation portion 32 c can also performaveraging of the first channel estimation value and second channelestimation value and similar to calculate a third channel estimationvalue and improve the channel estimation precision, and can input thisthird channel estimation value to the data channel demodulation portion32 d. On the other hand, if it is found that additional pilot symbolsare not included, the control channel demodulation portion 32 b issuesan instruction to the second channel estimation portion 32 c to inputthe first channel estimation value to the data channel demodulationportion 32 d.

When additional pilot symbols are not included, the data channeldemodulation portion 32 d performs data channel demodulation accordingto the first channel estimation value and the control symbol information(wireless link parameters and similar).

The error detection portion 33 detects the presence or absence of errorsin the data channel, and inputs the detection result to the ACK/NACKgeneration portion 34, and if there are no errors, outputs the datasymbols of the data channel. The ACK/NACK generation portion 34generates ACK/NACK based on the presence or absence of errors, andinputs the result to the control channel generation portion 35 a of theframe generation portion 35. The propagation path measurement portion 36uses the first channel estimation value measured by the first channelestimation portion 32 a of the demodulation portion 32 to measure thepropagation path state (reception SIR, received power, delay spread,Doppler frequency, and similar), and based on the measurement resultscreates propagation path information and inputs this to the controlchannel generation portion 35 a. If the channel estimation is A·exp(jθ),then the received power is |A|². The methods of measurement of thereception SIR, delay spread, Doppler frequency and similar arewell-known, and a detailed explanation is here omitted.

The control channel generation portion 35 a of the frame generationportion 35 generates control symbols comprising ACK/NACK and propagationpath information, the data channel generation portion 35 b generatesdata symbols, the basic pilot generation portion 35 c generates basicpilot symbols, and the multiplexing portion 35 d multiplexes and outputsthese symbols. Similarly to the transmission device, the receptiondevice can also execute control to add pilot symbols which are differentfrom the basic pilot symbols; but this explanation assumes that pilotaddition control is not performed. The transmission portion 37 performsorthogonal modulation using frames generated by the frame generationportion 35, up-converts the frequency of baseband transmission signalsthus obtained to the radio frequency and performs amplification, andtransmits the signals to the transmission device from the antenna 38.

FIG. 11 shows the flow of demodulation processing by the demodulationportion 32 in the reception device.

First, using basic pilot symbols included in a received frame, thepropagation path is estimated and a first channel estimation value isoutput (step 502). Then, this first channel estimation value is used todemodulate the control channel included in the received frame (step503), and based on control symbol information, a check is performed todetermine whether additional pilot symbols are included in the receivedframe (step 504); if no additional pilot symbols are included, the firstchannel estimation value is used to demodulate the data channel (step505).

On the other hand, if in step 504 the additional pilot symbols areincluded in the received frame, the additional pilot symbols are used toestimate the propagation path, and a second channel estimation value isoutput (step 506). Then, this second channel estimation value is used todemodulate the data channel (step 507).

The first channel estimation value and second channel estimation valuecan also be averaged or otherwise processed to calculate a third channelestimation value, to raise the channel estimation precision, and thethird channel estimation value can be used to demodulate the datachannel. When the fading frequency is high, the second channelestimation value estimated using additional pilot symbols in dispersedpositions may be used to demodulate the data channel, and when thefading frequency is low, the third channel estimation value may be usedfor data channel demodulation.

In the above, the transmission device uses the control channel to conveythe presence or absence of additional pilot symbols and the number ofsymbols, the positions at which symbols are added, and otherinformation, and so the reception device can identify the presence orabsence of additional pilot symbols, the number of symbols, and addedpositions, and can use the additional pilot symbols in channelestimation.

(d) Second Configuration of a Reception Device

When the control channel is divided into a portion comprising additionalpilot symbols information and another control information portioncomprising wireless link parameters, there are cases in which no errorsoccur in the additional pilot information, but errors occur in thecontrol information other than the additional pilot information. In suchcases, a channel estimation value estimated employing the additionalpilot symbols can be used to again perform demodulation of the controlchannel, to alleviate the control channel errors.

FIG. 12 is a second configuration of a reception device, with the abovecontrol channel errors alleviated; portions which are the same as in thereception device of FIG. 10 are assigned the same symbols. The differentpoint is the configuration of the demodulation portion 32 in which firstand second control channel demodulation portions 32 b ₁ and 32 b ₂ areprovided as control channel demodulation portions in the demodulationportion 32, and an error detection portion 32 e is provided.

In this embodiment, as shown in FIG. 13, the control channel is dividedinto an additional pilot information portion, and another controlinformation portion comprising wireless link parameters other thanadditional pilot information; error detection information (CRCinformation) is appended to the additional pilot information.

The first channel estimation portion 32 a performs channel estimationusing basic pilot symbols. The first control channel demodulationportion 32 b ₁ demodulates the control channel using the first channelestimation value and inputs the demodulation results to the errordetection portion 32 e. The error detection portion 32 e performs errordetection of additional pilot information included in the demodulationresults.

If no errors are detected in the additional pilot information, and theadditional pilot information indicates that additional pilot symbols areincluded, the first control channel demodulation portion 32 b ₁instructs the second channel estimation portion 32 c to execute channelestimation using the additional pilot symbols. As a result of thisinstruction, the second channel estimation portion 32 c uses theadditional pilot symbols to perform channel estimation, and inputs thesecond channel estimation value thus obtained to the data channeldemodulation portion 32 d and to the second control channel demodulationportion 32 b ₂.

By averaging the first channel estimation value and second channelestimation value to determine a third channel estimation value, thechannel estimation precision is improved, and the second control channeldemodulation portion 32 b ₂ and data channel demodulation portion 32 dcan be notified of the third channel estimation value thus obtained.

The second control channel demodulation portion 32 b ₂ again demodulatesthe control channel based on the channel estimation value obtained bythe second channel estimation portion 32 c, and notifies the datachannel demodulation portion 32 d of the adaptive wireless linkparameters and additional pilot symbol position information. The datachannel demodulation portion 32 d performs data channel demodulationbased on the second channel estimation value or third channel estimationvalue and on the control symbol information (wireless link parametersand additional pilot symbol position information, and similar).

Upon a judgment that additional pilot symbols are not included, thefirst control channel demodulation portion 32 b ₁ instructs the secondchannel estimation portion 32 c to input the first channel estimationvalue to the data channel demodulation portion 32 d.

In this way, when channel estimation using basic pilot symbols andcontrol channel demodulation using the first channel estimation valueare performed, if there are no transmission errors in the additionalpilot information, the additional pilot symbols can be used in channelestimation, and the resulting second channel estimation value can beused to again demodulate the control symbol portion; hence even whentransmission errors occur in control information other than additionalpilot information demodulated using the first channel estimation value,control symbols can be correctly demodulated using the second channelestimation value, so that transmitted data symbols can be correctlyreceived and demodulated.

FIG. 14 shows the flow of demodulation control processing of thedemodulation portion 32 in the reception device of FIG. 12.

First, the basic pilot symbols included in the received frame are usedto estimate the propagation path, and a first channel estimation valueis output (step 602). Then, this first channel estimation value is usedto demodulate the control channel included in the received frame (step603), and based on the control symbol information, detection of errorsin the additional pilot information is performed (step 604); if thereare errors, the first channel estimation value is used to demodulate thedata channel (step 605).

If there are no errors in the additional pilot information, a check isperformed for the existence of additional pilot symbols (step 606), andif none exist, the processing of step 605 is performed.

On the other hand, if in step 606 the additional pilot symbols exist,then the additional pilot symbols are used to estimate the propagationpath, and a second channel estimation value is output (step 607), thenthe control channel is demodulated again based on the second channelestimation value (step 608), and the adaptive wireless link parametersand additional pilot symbol position information are acquired, and datachannel demodulation is performed based on these values (step 609).

(C) Second Embodiment

FIG. 15 shows the configuration of the transmission device in a secondembodiment; the device has a configuration enabling both transmissionusing a single transmission antenna, and MIMO multiplexed transmission.

In the event of MIMO multiplexed transmission, the transmission deviceuses two transmission antennas 51, 52, transmitting independent datachannels from the transmission antennas 51, 52; when MIMO multiplexedtransmission is not performed, a data channel is transmitted only fromtransmission antenna 51.

The first frame generation portion 53 assembles a frame not comprisingadditional pilot symbols, to be transmitted from one transmissionantenna 51, and the second frame generation portion 54 assembles a frameto be transmitted from the other transmission antenna 52, comprisingadditional pilot symbols, but not comprising basic pilot symbols orcontrol symbols.

That is, the frame generation portion 53 comprises a basic pilotgeneration portion 53 a, which generates basic pilot symbols; a controlchannel generation portion 53 b, which generates control symbols; a datachannel generation portion 53 c, which generates data symbols; and amultiplexing portion 53 d, which multiplexes and outputs these symbols.When transmission is from a single transmission antenna 51 withoutperforming MIMO multiplexed transmission, the frame generation portion53 generates and outputs a frame such as in (A) of FIG. 16. Thetransmission portion 55 performs orthogonal modulation, frequencyup-converting and other wireless processing of the frame generated bythe frame generation portion 53, and transmits the frame from theantenna 51.

The frame generation portion 54 has a data channel generation portion 54a which generates data symbols, an additional pilot generation portion54 b which generates additional pilot symbols, and a multiplexingportion 54 c which multiplexes and outputs these symbols. Whenperforming MIMO multiplexing and transmission, the frame generationportion 54 generates and outputs frames such as in (C) of FIG. 16. Thetransmission portion 56 performs wireless processing of frames generatedby the frame generation portion 54, and transmits the frames from theantenna 52. During MIMO multiplexing and transmission, the framegeneration portion 53 generates and outputs frames with spaces made inadditional pilot symbol portions of the data symbol area, as shown in(B) of FIG. 16, and the transmission portion 55 performs wirelessprocessing and transmits the frames from the antenna 51. The controlsymbols are made to comprise information indicating whether MIMOmultiplexed transmission is being performed.

The adaptive wireless link control portion 57 executes control to decidethe data channel modulation method, coding rate, spreading factor, andother link parameters according to propagation path information receivedfrom the mobile terminal (receiving terminal) indicating the state ofthe propagation path, or propagation path information indicating thepropagation path state measured by a propagation path state measurementportion (not shown) within the transmission device, or ACK/NACKinformation received from the receiving terminal, and at the same timeinputs this information to the control channel generation portion 53 band data channel generation portions 53 c, 54 a. Further, when there isa high-speed transmission request from the receiving station, theadaptive wireless link control portion 57 inputs to the additional pilotallocation portion 58 an instruction to switch from transmission using asingle transmission antenna 51 to MIMO multiplexed transmission using aplurality of transmission antennas 51, 52.

When a MIMO multiplexed transmission instruction is input, theadditional pilot allocation portion 58 instructs the additional pilotgeneration portion 54 b to generate additional pilot symbols, providingthe number of additional pilot symbols and the additional pilot symbolpositions, and inputs the additional pilot symbol positions to the datachannel generation portions 53 c and 54 a. As a result, the framegeneration portion 53 generates a frame such as in (B) of FIG. 16, theframe generation portion 54 generates a frame such as in (C) of FIG. 16,and the frames are transmitted from the transmission antennas 51, 52.

The reception portion 59 receives signals sent from the reception devicevia the antenna 60, down-converts the frequency of the received radiosignals to the baseband frequency, and then performs orthogonaldemodulation and inputs the results to the channel estimation portion61, control channel demodulation portion 62, and data channeldemodulation portion 63. The channel estimation portion 61 uses pilotsymbols to estimate the uplink channel from the reception device (mobileterminal), and the control channel demodulation portion 62 uses thechannel estimation value to demodulate the control channel sent from thereception device, and notifies the adaptive wireless link controlportion 57 of propagation path information, ACK/NACK information,high-speed transmission requests, and similar transmitted via thecontrol channel. The data channel demodulation portion 63 uses thechannel estimation value as well as control information specifying themodulation method, coding rate and similar to demodulate and output datasymbols.

FIG. 17 shows the configuration of the reception device in the secondembodiment, configured to enable reception during transmission by asingle transmission antenna and reception during MIMO multiplexedtransmission.

The reception device uses two reception antennas 71, 72 during MIMOmultiplexed transmission, and the independent data channels transmittedfrom the transmission antennas 51, 52 are separated and output; whenMIMO multiplexed transmission is not performed, one reception antenna71, or two reception antennas 71, 72 are used, and the data channeltransmitted from the transmission antenna 51 is demodulated and output.

The reception portions 73, 74 down-convert the frequency of the radiosignals received by the reception antennas 71, 72 to the basebandfrequency, and then perform orthogonal demodulation of received frames.

If MIMO multiplexed transmission is not being performed, the firstchannel estimation portion 77 uses the basic pilot symbols included ineach of the received frames output from the reception portions 73, 74 toestimate the propagation paths from the transmission antenna 51 to thereception antennas 71, 72, to obtain channel estimation values h₀₀),h₁₀. The control channel demodulation portion 78 uses the channelestimation values h₀₀, h₁₀ thus obtained to perform demodulation of thecontrol channel of received frames input from the reception portions 73,74, and inputs control symbol information (wireless link parameters,whether MIMO multiplexed transmission is being performed, and similar)to the MIMO signal separation portion 75.

When MIMO multiplexed transmission is not being performed, the MIMOsignal separation portion 75 uses the above-described channel estimationvalues h₀₀, h₁₀ to demodulate data symbols in the data channeltransmitted from the transmission antenna 51, and inputs the results tothe error correction decoding portion 76.

If MIMO multiplexed transmission is being performed, the first channelestimation portion 77 uses basic pilot symbols included in each of thereceived frames output from the reception portions 73, 74 to estimatethe propagation paths from the transmission antenna 51 to the receptionantennas 71, 72, obtaining channel estimation values h₀₀, h₁₀. Thecontrol channel demodulation portion 78 uses the channel estimationvalues h₀₀, h₁₀ thus obtained to perform demodulation of the controlchannel of received frames input from the reception portions 73, 74, andfrom the control symbol information obtains information that MIMOmultiplexed transmission is being performed as well as additional pilotsymbols information, and instructs the second channel estimation portion79 to use the additional pilot symbols to perform channel estimation.Further, the control channel demodulation portion 78 inputs controlsymbol information (wireless link parameters and additional pilot symbolpositions, whether MIMO multiplexed transmission is being performed, andsimilar) to the MIMO signal separation portion 75.

The second channel estimation portion 79 estimates the propagation pathsfrom the transmission antenna 52 to the reception antennas 71, 72 usingthe additional pilot symbols, according to the instruction from thecontrol channel demodulation portion 78, and inputs the channelestimation values obtained h₀₁, h₁₁ to the MIMO signal separationportion 75. The MIMO signal separation portion 75 uses theabove-described channel estimation values h₀₀, h₁₀, h₀₁, h₁₁ to performwell-known MIMO signal separation processing, separates and demodulatesdata symbols in the data channel transmitted from the transmissionantennas 51, 52, and inputs the results to the error correction decodingportion 76.

According to the second embodiment, when transmitting from a pluralityof transmission antennas, additional pilot symbols are inserted, so thatchannel estimation necessary for data symbol demodulation can beperformed on the receiving side. Hence switching from transmission froma single transmission antenna to transmission from a plurality oftransmission antennas, as in the case of MIMO multiplexed transmission,is possible in response to a request.

Also, according to the second embodiment, pilots can be added toestimate the propagation path for each transmission antenna, so thatcommunication methods employing multi-antenna transmission techniquescan be flexibly accommodated. And, when not transmitting using multipleantennas, excess pilot symbols are not used, so that data transmissionefficiency can be improved.

(D) Third Embodiment

FIG. 18 shows the configuration of the transmission device of a thirdembodiment, capable of both transmission by only a single transmissionantenna, and of transmission using a plurality of antennas fortransmission-beam forming. The beam directionality of one antenna ANT1is nondirectional, as indicated by BD1 in FIG. 19, and the gain isconstant regardless of the direction from ANT1 to the mobile terminalMS. On the other hand, by means of an adaptive array antenna, thetransmission beam can be provided with the directionality BD2 andtransmission can be directed in a prescribed direction, so that comparedwith a case of nondirectional transmission by a single antenna, a highergain can be obtained. Hence when the mobile terminal MS becomes distantfrom the antenna ANT1 and reception quality declines, throughtransmission-beam forming to perform transmission from a plurality ofantennas with directionality, the reception quality can be improved.

The transmission device of FIG. 18 uses four transmission antennas 81 ato 81 d in transmission-beam forming; when not using transmission-beamforming, signals are transmitted only from the transmission antenna 81a.

The first frame generation portion 82 assembles frames comprising basicpilot symbols and control symbols to be transmitted from onetransmission antenna 81 a, and the second frame generation portion 83assembles frames to be transmitted from the transmission antennas 81 ato 81 d, not comprising basic pilot symbols or control symbols.

That is, the first frame generation portion 82 comprises a basic pilotgeneration portion 82 a, which generates basic pilot symbols; a controlchannel generation portion 82 b, which generates control symbols; and amultiplexing portion 82 c, which multiplexes and outputs these basicpilot symbols and control symbols with the data symbols output from thesecond frame generation portion 83.

The second frame generation portion 83 has a data channel generationportion 83 a, which generates data symbols; an additional pilotgeneration portion 83 b, which generates additional pilot symbols; and amultiplexing portion 83 c, which multiplexes and outputs these symbols.

When transmitting from a single transmission antenna 81 a withoutperforming transmission-beam forming, the first frame generation portion82 multiplexes basic pilot symbols, control symbols, and data symbolsfor the transmission antenna 81 a output from the beam former 85, andgenerates and outputs frames such as in (A) of FIG. 20. The transmissionportion 84 a performs wireless signal processing of frames generated bythe first frame generation portion 82 and second frame generationportion 83, and transmits the frames from antenna 81 a.

When performing beam forming and transmission, the second framegeneration portion 83 generates and outputs frames such as in (B) ofFIG. 20. The beam former 85 adds weighting to frames input to eachantenna such that the beam is directed in the direction of existence ofthe reception device. The first frame generation portion 82 multiplexesbasic pilot symbols, control symbols, and the symbols for thetransmission antenna 81 a output from the beam former 85 (data symbols,additional pilot symbols), and generates and outputs frames such as in(C) of FIG. 20. The transmission portion 84 a transmits frames generatedby the first frame generation portion 82 from the antenna 81 a, and thetransmission portions 84 b to 84 d transmit frames output from the beamformer 85 and with weighting from the respective antennas 81 b to 81 d.

The adaptive wireless link control portion 86 executes control to decidethe data channel modulation method, coding rate, spreading factor, andother link parameters based on propagation path information sent fromthe reception device, or on propagation path information indicating thepropagation path state measured by a propagation path state measurementportion (not shown) within the device itself, and at the same timeinputs this information to the control channel generation portion 82 band data channel generation portion 83 a. If link parameter modificationis not possible, the adaptive wireless link control portion 86 notifiesthe additional pilot allocation portion 87 of switching fromtransmission by a single transmission antenna to beam formingtransmission by a plurality of transmission antennas. By this means, theadditional pilot allocation portion 87 instructs the additional pilotgeneration portion 83 b to generate additional pilot symbols, andspecifies the number of additional pilot symbols and the additionalpilot symbol positions, and in addition inputs the additional pilotsymbol positions to the data channel generation portion 83 a, andnotifies the control channel generation portion 82 b of informationrelating to additional pilot symbols and of the fact that beam formingtransmission is being performed. As a result, the second framegeneration portion 83 generates frames such as shown in (B) of FIG. 20,the first frame generation portion 82 generates frames such as shown in(C) of FIG. 20, and the frames are transmitted from the transmissionantennas 81 a to 81 d.

The reception portion 88 receives signals sent from the reception devicevia the antenna 81 e, down-converts the frequency of the received radiosignals to the baseband frequency, and then performs orthogonaldemodulation and inputs the results to the channel estimation portion 89a, control channel demodulation portion 89 b, and data channeldemodulation portion 89 c. The channel estimation portion 89 a usespilot signals to estimate the uplink channel from the reception device(mobile terminal), and the control channel demodulation portion 89 buses the channel estimation value to demodulate the control channel sentfrom the reception device, and notifies the adaptive wireless linkcontrol portion 86 of propagation path information, ACK/NACKinformation, and similar transmitted via the control channel. The datachannel demodulation portion 89 c uses the channel estimation value andcontrol information which identifies the modulation method, coding rate,and other parameters to demodulate and output data symbols.

FIG. 21 shows the configuration of the reception device in the thirdembodiment; portions which are the same as in the reception device ofthe first embodiment in FIG. 10 are assigned the same symbols.Differences include (1) the fact that a channel estimation valueswitching portion 32 f is provided in the demodulation portion 32; (2)the fact that the first channel estimation portion 32 a estimates thepropagation path for transmission by a single transmission antenna andoutputs a first channel estimation value, and the second channelestimation portion 32 c estimates the propagation path for beam formingtransmission and outputs a second channel estimation value; and (3) thefact that the channel estimation value switching portion 32 f selectsthe first channel estimation value or the second channel estimationvalue, according to whether transmission is a single antennatransmission or is beam forming transmission, and inputs the selectedvalue to the data channel demodulation portion 32 d.

The first channel estimation portion 32 a uses basic pilot symbolsincluded in the received frames to perform channel estimation, andinputs the obtained first channel estimation values to the controlchannel demodulation portion 32 b and channel estimation value switchingportion 32 f. The control channel demodulation portion 32 b demodulatesthe control channel based on the first channel estimation value,determines whether the transmission is beam forming transmission, and ifthe transmission is beam forming transmission, confirms the number ofadditional pilot symbols and their positions, and instructs the secondchannel estimation portion 32 c to execute channel estimation using theadditional pilot symbols.

The control channel demodulation portion 32 b inputs informationindicating whether the transmission is beam forming transmission to thechannel estimation value switching portion 32 f, and notifies the datachannel demodulation portion 32 d of adaptive wireless link parametersand additional pilot symbol position information.

As a result of the instruction from the control channel demodulationportion 32 b, the second channel estimation portion 32 c performschannel estimation using the additional pilot symbols, and inputs thesecond channel estimation value thus obtained to the channel estimationvalue switching portion 32 f.

The channel estimation value switching portion 32 f selects one amongthe first channel estimation value and second channel estimation valueaccording to whether the transmission is a single antenna transmissionor beam forming transmission, and inputs the value to the data channeldemodulation portion 32 d. The data channel demodulation portion 32 dperforms data channel demodulation based on the input channel estimationvalue, wireless link parameters, additional pilot symbol positions, andsimilar.

By means of the above-described third embodiment, pilots can be addedfor use in estimating the propagation path of beam-formed signals, sothat communication methods using beam forming transmission techniquescan be flexibly accommodated. Moreover, when beam forming transmissionis not performed, excess pilot symbols are not used, so that datatransmission efficiency can be improved.

Thus by means of this invention, insertion of additional pilot symbolsis performed adaptively based on the propagation path state, so thatchannel estimation precision can be improved.

By means of this invention, even when the motion velocity of the mobilestation is fast and the fading frequency is high, by dispersing thepositions of the additional pilot symbols, the channel estimationprecision can be adaptively improved.

By means of this invention, when data errors are not alleviated byadaptive control which changes the transmission method based on thepropagation path state, pilot symbols are added, so that the S/N of datasymbol can be improved, and moreover the precision of channel estimationcan simultaneously be improved through pilot addition.

By means of this invention, additional pilot symbols are inserted whentransmitting from a plurality of transmission antennas, so that channelestimation necessary for demodulation of data symbols can be performedon the receiving side. Hence switching can be performed, based on thepropagation path state or on request from the receiving side, fromtransmission by a single transmission antenna to transmission by aplurality of transmission antennas, such as in MIMO multiplexedtransmission and in transmission-beam forming. That is, by means of thisinvention, pilots can be added to estimate the propagation paths ofsignals for each transmission antenna and the propagation paths ofsignals transmitted by beam forming, so that communication methodsemploying multi-antenna transmission techniques can be flexiblyaccommodated. Further, when transmission employing multiple antennas isnot performed, excess pilot symbols are not used, so that datatransmission efficiency can be improved.

By means of this invention, the control channel is used to convey thepresence or absence of additional pilot symbols, the number of suchsymbols, the added positions, and other information, so that on thereceiving side the presence or absence of additional pilot symbols, thenumber of symbols, and the positions of addition can be recognized, andthe additional pilot symbols can be used in channel estimation.

By means of this invention, in addition to adaptive wireless linkcontrol of the data channel, additional pilot symbol addition control isperformed, so that not only the S/N of the data channel, but theprecision of channel estimation can also be improved simultaneously, andsystem throughput can be enhanced.

By means of this invention, the additional pilot symbol power and numberof symbols can be set to small values in advance, so that pilot symbolinsertion losses can be kept low. By this means, throughput at celledges can be improved, and interference in other cells can be reduced.

By means of this invention, by detecting errors in additional pilotinformation included in the control channel, even when transmissionerrors occur in the control channel other than the additional pilotinformation, the result of channel estimation using additional pilotsymbols can be employed to again execute control symbol decoding, sothat control channel transmission errors can be alleviated.

What is claimed is:
 1. A wireless communication system for transmittingand receiving frames comprising basic pilot symbols used commonly forone or more reception devices which communicate with a transmissiondevice, in propagation path estimation, control symbols conveyingcontrol information used for data channel demodulation, and data symbolsconveying information bits, wherein the transmission device comprises: apilot addition decision portion for deciding whether to add pilotsymbols and a position of additional pilot symbols, which are separatefrom the basic pilot symbols, to frames; a control symbol generationportion for generating control symbols comprising information indicatingwhether the additional pilot symbols are present and the position of theadditional pilot symbols; a frame assembly portion for assembling framesto which said pilot symbols are added according to said pilot additiondecision; and a transmission portion for transmitting the frames; andthe reception device comprises: a control symbol demodulation portionfor demodulating control symbols included in the received frames, andjudges whether the additional pilot symbols symbols are included in thereceived frames based on the control symbol information; and a datasymbol demodulation portion for demodulating data symbols based on apropagation path estimation value which is estimated using theadditional pilot symbols or using the additional pilot symbols and thebasic pilot symbols when the additional pilot symbols are included inthe received frame.
 2. The wireless communication system according toclaim 1, wherein said transmission device comprises a propagation pathinformation output portion, which acquires and outputs propagation pathinformation relating to a state of the propagation path between thereception device and the transmission device, and said pilot additiondecision portion decides on whether it is necessary to add said pilotsymbols, and on a number of additional pilot symbols based on thepropagation path information.
 3. The wireless communication systemaccording to claim 1, wherein said transmission device comprises amotion velocity acquisition portion which acquires the motion velocityof the reception device, and said pilot addition decision portiondecides whether to arrange the additional pilot symbols in dispersedpositions in a data symbol area and positions of the additional pilotsymbols, according to the motion velocity of the reception device. 4.The wireless communication system according to claim 1, wherein saidtransmission device further comprises: a propagation path informationoutput portion which acquires and outputs propagation path informationrelating to a state of the propagation path between the reception deviceand the transmission device, and an adaptive control portion whichadaptively controls a transmission method based on said propagation pathinformation, wherein said pilot addition decision portion decides to addpilot symbols when transmission errors are not improved by the adaptivecontrol.
 5. The wireless communication system according to claim 1,wherein said transmission device comprises: a plurality of transmissionantennas, and a transmission portion corresponding to the respectivetransmission antennas, wherein said frame assembly portion assemblesframes comprising the basic pilot symbols and the control symbols butnot comprising the additional pilot symbols when transmitting from onetransmission antenna, and assembles said frames for transmission fromsaid one transmission antenna and frames for transmission from othertransmission antennas, comprising the additional pilot symbols butcomprising neither basic pilot symbols nor control symbols whentransmitting from the plurality of antennas.
 6. The wirelesscommunication system according to claim 5, wherein said reception devicecomprises: a plurality of reception antennas; a reception portioncorresponding to the respective reception antennas; and a propagationpath estimation portion for estimating the propagation paths from saidone transmission antenna to each reception antenna using the basic pilotsymbols and estimating the propagation paths from said othertransmission antennas to each reception antenna using said additionalpilot symbols, wherein the data symbol demodulation portion demodulatesdata symbols transmitted from each transmission antenna using apropagation path estimation value for each of said propagation paths. 7.The wireless communication system according to claim 1, wherein saidtransmission device comprises: a plurality of transmission antennas; atransmission portion corresponding to the respective transmissionantennas; a second frame assembly portion which, when pilot symbols areadded, assembles frames comprising the additional pilot symbols and datasymbols, but comprising neither basic pilot symbols nor control symbols;a beam former, which performs beam forming processing on the framesassembled by said second frame assembly portion and inputs results tothe respective transmission antennas; and a first frame assemblyportion, which assembles frames comprising basic pilot symbols, controlsymbols, and data symbols input from said beam former and inputs theframes to one transmission antenna, and wherein when beam forming is notperformed, said second frame assembly portion assembles frames withoutadding pilot symbols and inputs the frames to said one transmissionantenna, and when beam forming is performed, said second frame assemblyportion assembles frames with pilot symbols added and inputs signalsprocessed by said beam former to said plurality of transmissionantennas.
 8. The wireless communication system according to claim 7,wherein in a case where pilot symbols are not added, said first frameassembly portion assembles frames comprising basic pilot symbols,control symbols and data symbols and inputs the frames to said onetransmission antenna, and in a case where pilot symbols are added, thefirst frame assembly portion assembles frames comprising basic pilotsymbols, control symbols, and additional pilot symbols and data symbolsweighted by said beam former and inputs the frames to said onetransmission antenna.
 9. The wireless communication system according toclaim 7, wherein said reception device comprises: a plurality ofreception antennas; a reception portion corresponding to said respectivereception antennas; and a propagation path estimation portion forestimating the propagation path for transmission by said onetransmission antenna using said basic pilot symbols and estimating thepropagation paths for beam forming transmission using said additionalpilot symbols, wherein said control symbol demodulation portion judgeswhether beam forming transmission is being performed, and said datasymbol demodulation portion demodulates data symbols using a prescribedestimation value for said propagation path, according to whether beamforming transmission is being performed.
 10. The wireless communicationsystem according to claim 1, wherein said reception device comprises: afirst propagation path estimation portion which estimates thepropagation path using said basic pilot symbols, and a secondpropagation path estimation portion which, if the additional pilotsymbols exist, estimates the propagation path using the additional pilotsymbols, and wherein said control symbol demodulation portion as a firstcontrol symbol demodulation portion, demodulates control symbols using afirst propagation path estimation value estimated by said firstpropagation path estimation portion, and said data symbol demodulationportion, when said additional pilot symbols exist, demodulates datasymbols using said control symbol information and a second propagationpath estimation value estimated by said second propagation pathestimation portion, and said data symbol demodulation portion, when saidadditional pilot symbols do not exist, demodulates data symbols usingsaid control symbol information and a first propagation path estimationvalue estimated by said first propagation path estimation portion. 11.The wireless communication system according to claim 10, wherein saidreception device comprises: an error detection portion which detectserrors in the additional pilot symbol information included in saidcontrol symbols; and a second control symbol demodulation portion which,if no transmission errors have occurred in the additional pilot symbolinformation, demodulates control symbols again based on said secondpropagation path estimation value, and wherein said data symboldemodulation portion, when no transmission errors have occurred in theadditional pilot symbol information, demodulates data symbols using thecontrol symbols demodulated by said second control symbol demodulationportion and said second propagation path estimation value and said datasymbol demodulation portion, when transmission errors have occurred inthe additional pilot symbol information, demodulates data symbols usingthe control symbols demodulated by said first control symboldemodulation portion and said first propagation path estimation value.12. A transmission device, in a wireless communication system fortransmitting and receiving frames comprising basic pilot symbols usedcommonly for one or more reception devices which communicate with thetransmission device, in propagation path estimation, control symbolsconveying control information used for data channel demodulation, anddata symbols conveying information bits, wherein comprising: a pilotaddition decision portion for deciding whether to add pilot symbols anda position of additional pilot symbols, which are separate from thebasic pilot symbols, to frames; a control symbol generation portion forgenerating control symbols comprising information indicating whether theadditional pilot symbols are present and the position of the additionalpilot symbols; a frame assembly portion assembling frames to which thepilot symbols are added according to said pilot symbol additiondecision; and a transmission portion transmitting the frames to areception device.
 13. The transmission device according to claim 12,further comprising a propagation path information output portion whichacquires and outputs propagation path information relating to a state ofthe propagation path between the reception device and the transmissiondevice, wherein said pilot addition decision portion decides on whethersaid pilot symbols are to be added, and on a number of additional pilotsymbols, based on the propagation path information.
 14. The transmissiondevice according to claim 13, further comprising a motion velocityacquisition portion which acquires the motion velocity of the receptiondevice, wherein said pilot addition decision portion decides whether toarrange the additional pilot symbols in dispersed positions in a datasymbol area and positions of the additional pilot symbols, according tothe motion velocity of the reception device.
 15. The transmission deviceaccording to claim 12, further comprising: a propagation pathinformation output portion which acquires and outputs propagation pathinformation relating to a state of the propagation path between thereception device and the transmission device, and an adaptive controlportion which adaptively controls a transmission method based on saidpropagation path information, wherein said pilot addition decisionportion decides to add pilot symbols when transmission errors are notimproved by the adaptive control.
 16. The transmission device accordingto claim 12, further comprising: a plurality of transmission antennas,and a transmission portion corresponding to the respective transmissionantennas, wherein said frame assembly portion assembles framescomprising basic pilot symbols and control symbols but not comprisingthe additional pilot symbols when transmitting from one transmissionantenna, and assembles said frames for transmission from said onetransmission antenna and frames for transmission from other transmissionantennas, comprising the additional pilot symbols but comprising neitherbasic pilot symbols nor control symbols when transmitting from theplurality of antennas.
 17. The transmission device according to claim12, further comprising: a plurality of transmission antennas; atransmission portion corresponding to the respective transmissionantennas; a second frame assembly portion which, when pilot symbols areadded, assembles frames comprising the additional pilot symbols and datasymbols, but comprising neither basic pilot symbols nor control symbols;a beam former, which performs beam forming processing on framesassembled by said second frame assembly portion and inputs results tothe respective transmission antennas; and a first frame assemblyportion, which assembles frames comprising basic pilot symbols, controlsymbols, and data symbols input from said beam former, and inputs theframes to one transmission antenna, wherein when beam forming is notperformed, said second frame assembly portion assembles frames withoutadding pilot symbols and transmits the frames from said one transmissionantenna, and when beam forming is performed, said second frame assemblyportion assembles frames with pilot symbols added, and transmits signalsprocessed by said beam former from said plurality of transmissionantennas.
 18. A reception device, in a wireless communication system fortransmitting and receiving frames comprising basic pilot symbols used inpropagation path estimation, control symbols conveying controlinformation necessary for data channel demodulation, and data symbolsconveying information bits, comprising: a reception portion receivingframes transmitted from a transmission device; a first propagation pathestimation portion which estimates the propagation path using the basicpilot symbols in said received frames and outputs a first propagationpath estimation value; a first control symbol demodulation portion whichdemodulates control symbols comprising information indicating whetheradditional pilot symbols are present and a position of the additionalpilot symbols, by using the propagation path estimation value, andjudges from the control symbol information whether the additional pilotsymbols are added to the received frames and the position of theadditional pilot symbols; a second propagation path estimation portionwhich, when the additional pilot symbols are added, estimates thepropagation path using the additional pilot symbols and outputs a secondpropagation path estimation value; and a data symbol demodulationportion which, when the additional pilot symbols are not added toframes, demodulates data symbols using said first propagation pathestimation value, but when the additional pilot symbols are added,demodulates data symbols using said second propagation path estimationvalue.
 19. The reception device according to claim 18, furthercomprising: an error detection portion, which detects errors in theadditional pilot symbol information included in said control symbols;and a second control symbol demodulation portion which, if notransmission errors have occurred in the additional pilot symbolinformation, demodulates control symbols again based on said secondpropagation path estimation value, wherein said data symbol demodulationportion, when no transmission errors have occurred in the additionalpilot symbol information, demodulates data symbols using control symbolsdemodulated by said second control symbol demodulation portion and saidsecond propagation path estimation value and said data symboldemodulation portion, when transmission errors have occurred in theadditional pilot symbol information, demodulates data symbols usingcontrol symbols demodulated by said first control symbol demodulationportion and said first propagation path estimation value.
 20. A wirelesscommunication method for transmitting and receiving frames comprisingbasic pilot symbols used commonly for one or more receiving sides whichcommunicate with a transmitting side, in propagation path estimation,control symbols conveying control information used for data channeldemodulation, and data symbols conveying information bits, comprising,on the transmitting side: deciding whether to add pilot symbols and aposition of additional pilot symbols which are separate from the basicpilot symbols, to frames; generating control symbols comprisinginformation indicating whether the additional pilot symbols are presentand the position of the additional pilot symbols; and assembling andtransmitting frames comprising said basic pilot symbols, controlsymbols, additional pilot symbols, and data symbols; and comprising, onthe one or more receiving sides; demodulating control symbols includedin the received frames; judging whether the received frames comprise theadditional pilot symbols based on the control symbol information; whenthe additional pilot symbols are included, estimating the propagationpath using the additional pilot symbols or using the additional pilotsymbols and the basic pilot symbols; and demodulating data symbols usingthe propagation path estimation value.
 21. The wireless communicationmethod according to claim 20, wherein the deciding includes: acquiringpropagation path information and deciding on whether said pilot symbolsare to be added, and on a number of additional pilot symbols, based onthe propagation path information.
 22. The wireless communication methodaccording to claim 20, wherein the deciding includes: acquiring motionvelocity of the one or more receiving sides, and deciding whether toarrange the additional pilot symbols in dispersed positions in a datasymbol area and positions of the additional pilot symbols according tothe motion velocity of the one or more receiving sides.
 23. The wirelesscommunication method according to claim 20, wherein, the method furthercomprises: acquiring and outputting propagation path informationrelating to a state of the propagation path between the one or morereceiving sides and the transmitting side, and adaptively controlling atransmission method based on said propagation path information, whereinin said deciding, when transmission errors are not improved even by theadaptive control, a decision is made to add pilot symbols.
 24. Areception device, in a wireless communication system for transmittingand receiving frames comprising basic pilot symbols used commonly forone or more reception devices which communicate with a transmissiondevice, in propagation path estimation, control symbols conveyingcontrol information used for data channel demodulation, and data symbolsconveying information bits, comprising, a reception portion receivingframes transmitted from the transmission device; a control symboldemodulation portion which demodulates control symbols comprisinginformation indicating whether additional pilot symbols are present anda position of the additional pilot symbols, included in the receivedframes and judges based on the control symbol information whether theadditional pilot symbols are included in the received frames and theposition of the additional pilot symbols wherein the additional pilotsymbols being added to frames separately from the basic pilot symbols,in the transmission device; and a data symbol demodulation portion fordemodulating data symbols based on a propagation path estimation valuewhich is estimated using the additional pilot symbols or using theadditional pilot symbols and basic pilot symbols when the additionalpilot symbols are included in the received frame.